Aceto



Patented Dec. 15.1953

UNITED oFFICE Delaware Application September a, 1952, Serial No. 308,484 1 This invention relates to an improved method of purifying crude acetone. More particularly, it relates to a method of purifying crude' acetcne containing :small bu-tzsignificant quantities of mesityl oxide'and aldehyde:impurities.- 1 'Jf Crude acetone prepared by catalytic processe contains acetone-water, and small-quantities of other lower and'higher boiling carbonyl impurities,- including mesityl oxide and aldehyde impurities, i. e., propion-= and acetaldehyde. These impurities, especially'the mesityl oxide and aldehyde ones, though present in small quantities. are extremely difficult to remove by conventional means of fractionation. i. They cause the product to have a low permanganate test time and contain more than 0.005 weight per cent aldehydes calculated as formaldehyde. The product is consequently unsatisfactory because: i

1. Acetone with an objectionable odor is not suited for use in paint and'varnish'reinovers preparing coated fabrics; manufacture of, paints, varnishes, and lacquers.

4 Claims. (01. 2,02-.-a9.5)

2. The presence of aldehydes and other sube stances which reduce permanganate time of acetone renders this materialunsuitable for.

use in manufacturing photographic films.

3. Acetone containing aldehydes is unsuitable for H use in the production of penicillin.

(Chemically pure acetone is defined as having a boiling range between 56-5S C. and a permanganate test time of at least thirty minutes and" less than 0.005% aldehydes as formaldehyde.)

s's t d ab ve. nv n ional fractionation to purify the crude acetone suffers from distinct difficulties, i. e., the high expense because of high reflux ratios required and- 10w yields ofproduct chemically meeting the desired specification for pure acetone.

Purification by water extractive distillation also presents certain difiiculties. Thus,zin order to obtain maximum yield of C. -P. acetone from r a given crude by this manner of distillation it-is necessary to use a volumetric-solvent to feed ratio v of 17.5 to 1. This makes theprocess extremely expensive, in terms of both utilities and equip.-

This invention provides an improved method'of purifying the crude acetone. The method com prises caustic treating the crude acetone under carefully controlled conditions followed by frac tionally distilling the caustic treated acetone in a distillation zone wherein water is added above thecaustic treated crude acetonefeed point. The conditions of the latter distillation are also carefully controlled. I I I v The crude acetonefeed ofthis invention contains predominantly acetone, i.- e., -90 weight per cent and usually--90 weight per cent, and minor proportions of water; mesityl oxide, and aldehydes. Asexplained above, the mesityl oxide and aldehyde impurities, even though present in verysmallquantities, accountfor the greatest difilculty inthe acetone purification. A typical feed analysis is listed below in Table 1.

v JTII'ABLEVVI 86.8 weightper cent acetone 2.3*weight percentwater w 0.5 weight-per cent mesityl oxide impurities 10.3 weight per cent isopropanol. I I

Thecaustic treat, i. e., with aqueous sodium and aldehyde hydroxide or potassium hydroxide, is carried out under the, following conditions:

Weight percent hydroxide in watch... 20-50. Preferred treating time 15 minutes to 3 hours. Temperature. Atmospheic, i. e., about high, the yield ofC'. P. acetonewill be low. This is shown in Table'3 below.

TABLE 2. 40

-Vo lumet-. I ric ratio Contact crude ace- Vol. per- Trcat, weight percent N aOH time tone to cent acel v (hrs) aqueous tone lost caustic solution 18 1:1 5. 3 3 1:1 "3. 0 1:1 2. 9 lzl 1.8 )4 1:1 1; l

TABLE 3 Efl'ect of volume of 35% caustic used in pre-treat upon yield of C. P. acetone Pro-treat Extractive distillation column Product column 0. P. ace- Vol. ratio Vol. ratio Heads tone yield NaOH Contact caustic S went solvent cut, vol. No. of Ext. re- Plates Ext. rc based on solution time solution to feed percent plates flux ratio flux ratio that to feed ratio of feed acetone in crude 1:1 Tap water 5.0:1 3.0 55 0:1 70 8:1 94.3 1:2 do 52:1 3.1 55 0:1 70 8:1 96.9 1:9 r do 5. 2:1 3.0 55 0:1 70 8:1 80.2

The specified distillation in the presence of water is also carried out under well-defined conditions:

Ratio of water/feed v./v 2-8/1 Overhead traction 2-10 volume per cent organics based on the organics originally present in the feed. Pressure Atmospheric.

This invention will be better understood by reference to the flow diagram shown in the drawmg.

In the system shown aqueous 35 weight per cent sodium hydroxide solution flows through line I into mixing and settling tank 3. Crude acetone in a volume equal to twice the volume of the aqueous caustic enters tank 3 through linel. The two liquid systems are intimately contacted in tank'3 and allowed to settle int an upper or ganic phase and a lower aqueous caustic phase. The latter is withdrawn from tank 3 through line 4 and recycled to line I. Experimental data indicate that the predominant proportion of the undesirable carbonyl impurities is not removed with the caustic by line 4, but rather converted to a form which can be readily removed in the subsequent distillation. The carbonyl impurities are apparently converted to highermolecular weight products which are more easily ejected overhead in the subsequent distillation.

The separated organic crude caustic treated acetone phase may be preheated if desired to below its boiling point, e. g., to a temperature of tion of acetone tutes an internal liquid reflux ascending countercurrently through the vapors undergoing rectification at an upper part of th tower. The vapors passing overheard through line I at a temperature of about 90 C. include in this head cut 2 to lfl'volume per cent organics based on the organics in the crude acetone feed. This cut therefore contains substantially all the mesityl oxide, some acetone, substantially all the aldehydes, and some alcohol. It is mostly water, containing 5 to 6 volume-per cent organics. The temperature in the intermediate portion of the tower is about 74 C. and about 80.9 C. at the lower portion. The bottoms withdrawn from tower 6 through line 8 contains acetone, alcohol and water, and is passed to a second fractionation tower l3. C. P. acetone is taken overhead through line H at a vapor temperature of 56- 58 C. (may go up to about 0.). The alcohol and water are withdrawn from tower [3 through line l0.

' The following examples further point out the advantages of this invention.

EXAMPLE I A comparison was made of conventional distillation, water extractive distillation and the combination process of this invention in the purification of crude acetone. The results are tabulated below in Table 4.

TABLE 4 Comparison of caustic pre-treat water extractive distillation with conventional distillation and with water extractive distillation for purifica- I C. P. acetone 1 d t yield-sigh; ro uc percent use Pre treat Beads column extractive distillation column on weight of acetone in feed V l V 1 Heat(18 0 o cu Contact ratio ratio vol. No. of No s lutlon Solvent reflux reflux time soda solvent perplates lates to feed to feed cent p of Iecd 1:1 'Tapwater... 2.0 6.2 55 0:1 40 8:1 72.9 89.3 None... None Dist. water.. 2.0 6. 2 55 0:1 40 8:1 53.1 84. 9 Conventioualdistillat do None None 5.6 55 5:1 40 I 8:1 7i. 7

l Yield of purer than C. P. acetone based on 5% outs in which acetone had a permanganate stability of 120+ minutes. 3 Yield of C. P. acetone based on blending cuts to give maxuuum yield of O. P. acetone.

56 C., and is fed through line 5, into fractional distillation zone 6. The water concentration -of 5 to l is efiected by introduction of water into an upper portion of tower 6 through line l2,

These results clearly show the decided improvement in yield of GP. acetone or yield of purer than C. P. acetone obtained through the process of this invention as compared with the two other which is above feed point 5; The waterconstimeans of operation.

EXAMPLE II A further comparison was made of the process of this invention utilizing optimum conditions with only water extractive distillation also utilizing optimum conditions for the latter. The results are presented below.

TABLE 5 to feed ratio in the range of 28/1 distilling from said distillation zone a vaporous mixture ascending countercurrent to the liquid water internal reflux; removing from the distillation zone a distillate comprising a predominant proportion of water containing substantially all the carbonyl Comparison of optimum caustic pre-treat water extractive distillation with optimum water extractive distillaiionfor purifying crude acetone Pie-treat Extractive distillation column Product column Q P tgne (yield Vol ratio Heads ase on Volumetric weight of Contact caustic vol. per- Number Ext. re- Ext. resolutmn time solution solvent solvent to cent of of plates flux ratio Plates flux ratio acetone m feed ratio crude to feed feed None None... None Tap water 17. 5:1 3.0 55 :1 70 8:1 93. 35% NaOH 3 hr .do 5. 2:1 3.1 55 0:1 70 8:1 96. 9

Two points should be noted. The yield of C. P.

pared to the process of this invention. Thus,

despite the much greater cost of the former, the results, if anything, were inferior.

It will be understood further that the foregoing examples have been given merely for purposes of illustration, but that other modifications of the invention are possible without departing from the scope of the claims.

What is claimed is:

1. A process for purifying acetone in a crude minor but significant proportion of carbonyl impurities including mesityl oxide and aldehydes, said feed being difficult to purify by conventional distillation, which comprises the steps of treating the crude feed with an aqueous caustic solution containing about -45 weight per cent caustic for a time of fifteen minutes to three hours with an aqueous caustic to feed ratio of 2/1 to 1/10; feeding the caustic treated mixture to a fractional distillation zone at an intermediate point thereof;

continuously adding water to the fractional distillation zone substantially above the feed point of the mixture to maintain a volumetric solvent impurities and some acetone, and withdrawing as a bottoms fraction from the fractional distillation zone acetone and water, free of carbonyl impurities.

2. The process of claim 1, including the additional step of distilling the bottoms fraction withdrawn from the fractional distillation zone so as to take overhead a pure acetone fraction.

3. The process of claim 1 in which the vaporous mixture distilled from the distillation zone contains from 2 to 10 volume per cent organic matter based on the organic matter present in the original crude feed.

4. The process of claim 1 in which the carbonyl impurities are lower and higher boiling than the acetone. feed containing predominantly acetone and a WILLIAM G. EMERSON, JR. JOSEPH R. QUELLY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,238,016 Downey Apr. 8, 1941 2,254,615 McAllister Sept. 2, 1941 2,485,615 Steele et a1 Sept. 2, 1941 2,533,754 Ballard Dec. 12, 1950 2,575,244 Carlson Nov. 13, 1951 2,615,812 Kaufiman Oct. 28, 1952 2,624,699 Joris Jan. 6, 1953 

1. A PROCESS FOR PURIFYING ACETONE IN A CRUDE FEED CONTAINING PREDOMINANTLY ACETONE AND A MINOR BUT SIGNIFICANT PROPORTION OF CARBONYL IMPURITIES INCLUDING MESITYL OXIDE AND ALDEHYDES, SAID FEED BEING DIFFICULT TO PURIFY BY CONVENTIONAL DISTILLATION, WHICH COMPRISES THE STEPS OF TREATING THE CRUDE FEED WITH AN AQUEOUS CAUSTIC SOLUTION CONTAINING ABOUT 30-45 WEIGHT PER CENT CAUSTIC FOR A TIME OF FIFTEEN MINUTES TO THREE HOURS WITH AN AQUEOUS CAUSTIC TO FEED RATIO OF 2/1 TO 1/10 FEEDING THE CAUSTIC TREATED MIXTURE TO A FRACTIONAL DISTILLATION ZONE AT AN INTERMEDIATE POINT THEREOF; CONTINUOUSLY ADDING WATER TO THE FRACTIONAL DISTILLATION ZONE SUBSTANTIALLY ABOVE THE FEED POINT OF THE MIXTURE TO MAINTAIN A VOLUMETRIC SOLVENT TO FEED RATIO IN THE RANGE OF 2-8/1; DISTILLING FROM SAID DISTILLATION ZONE A VAPOROUS MIXTURE ASCENDING COUNTERCURRENT TO THE LIQUID WATER INTERNAL REFLUX; REMOVING FROM THE DISTILLATION ZONE A DISTILLATE COMPRISING A PREDOMINANT PROPORTION OF WATER CONTAINING SUBSTANTIALLY ALL THE CARBONYL IMPURITIES AND SOME ACETONE, AND WITHDRAWING AS A BOTTOMS FRACTION FROM THE FRACTIONAL DISTILLATION ZONE ACETONE AND WATER, FREE OF CARBONYL IMPURITIES. 